Intraoperative radiation therapy using mobile electron linear accelerators:
Report of AAPM Radiation Therapy Committee Task Group No. 72
A. Sam Beddara兲
Department of Radiation Physics, Division of Radiation Oncology, Unit 94, The University of Texas M.D.
Anderson Cancer Center, Houston, Texas 77030
Peter J. Biggs
Department of Radiation Oncology, Massachusetts General Hospital, Boston, Massachusetts 02114
Sha Chang
Department of Radiation Oncology, University of North Carolina School of Medicine, Chapel Hill,
North Carolina 27599
Gary A. Ezzell
Department of Radiation Oncology, Mayo Clinic Scottsdale, Scottsdale, Arizona 85259
Bruce A. Faddegon
Department of Radiation Oncology, University of California San Francisco, San Francisco,
California 94143
Frank W. Hensley
Department of Radiation Oncology, University of Heidelberg, 69120 Heidelberg, Germany
Michael D. Mills
Department of Radiation Oncology, James Graham Brown Cancer Center, Louisville, Kentucky 40202
共Received 16 September 2005; revised 10 March 2006; accepted for publication 15 March 2006;
published 28 April 2006兲
Intraoperative radiation therapy 共IORT兲 has been customarily performed either in a shielded operating suite located in the operating room 共OR兲 or in a shielded treatment room located within the
Department of Radiation Oncology. In both cases, this cancer treatment modality uses stationary
linear accelerators. With the development of new technology, mobile linear accelerators have recently become available for IORT. Mobility offers flexibility in treatment location and is leading to
a renewed interest in IORT. These mobile accelerator units, which can be transported any day of use
to almost any location within a hospital setting, are assembled in a nondedicated environment and
used to deliver IORT. Numerous aspects of the design of these new units differ from that of
conventional linear accelerators. The scope of this Task Group 共TG-72兲 will focus on items that
particularly apply to mobile IORT electron systems. More specifically, the charges to this Task
Group are to 共i兲 identify the key differences between stationary and mobile electron linear accelerators used for IORT, 共ii兲 describe and recommend the implementation of an IORT program within
the OR environment, 共iii兲 present and discuss radiation protection issues and consequences of
working within a nondedicated radiotherapy environment, 共iv兲 describe and recommend the acceptance and machine commissioning of items that are specific to mobile electron linear accelerators,
and 共v兲 design and recommend an efficient quality assurance program for mobile systems. © 2006
American Association of Physicists in Medicine. 关DOI: 10.1118/1.2194447兴
TABLE OF CONTENTS
I. INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . .
II. IORT USING MOBILE VERSUS STATIONARY
LINEAR ACCELERATORS. . . . . . . . . . . . . . . . . . .
III. IMPLEMENTATION OF AN IORT PROGRAM
WITHIN AN OPERATING ROOM
ENVIRONMENT. . . . . . . . . . . . . . . . . . . . . . . . . . .
IV. RADIATION PROTECTION. . . . . . . . . . . . . . . . . .
A. Regulatory considerations. . . . . . . . . . . . . . . .
B. Radiation site plan. . . . . . . . . . . . . . . . . . . . . .
1. Treatment operating rooms. . . . . . . . . . . . .
2. Commissioning and annual quality
assurance location. . . . . . . . . . . . . . . . . . . .
1476
Med. Phys. 33 „5…, May 2006
1477
1477
1478
1478
1479
1479
1479
1479
C. Radiation survey. . . . . . . . . . . . . . . . . . . . . . . .
D. Exposure rate measurements. . . . . . . . . . . . . .
V. ACCEPTANCE TESTING AND
COMMISSIONING. . . . . . . . . . . . . . . . . . . . . . . . . .
A. Acceptance testing measurements. . . . . . . . . .
B. Commissioning and dose measurements. . . . .
VI. RECOMMENDED QUALITY ASSURANCE. . . .
A. Previous quality assurance recommendations
for medical linear accelerators. . . . . . . . . . . . .
B. Quality assurance for mobile electron
accelerators. . . . . . . . . . . . . . . . . . . . . . . . . . . .
VII. CLINICAL ASPECTS OF IORT TREATMENT
DELIVERY: DOSE SPECIFICATION. . . . . . . . .
VIII. RECOMMENDATIONS FOR FUTURE
CONSIDERATIONS. . . . . . . . . . . . . . . . . . . . . . .
0094-2405/2006/33„5…/1476/14/$23.00
© 2006 Am. Assoc. Phys. Med.
1479
1479
1480
1480
1482
1484
1484
1484
1486
1487
1476
1477
Beddar et al.: Task Group No. 72
I. INTRODUCTION
Intraoperative radiation therapy 共IORT兲 has had a long history in cancer management. The earliest concept of IORT as
a cancer treatment modality was introduced in 1909, when
Carl Beck attempted to treat patients with gastric and colon
cancer.1 Beck irradiated seven patients with inoperable gastric cancer and one patient with colon cancer by pulling the
tumor into the abdominal wound and irradiating it. The treatments were unsuccessful due to low beam energies, low dose
rates, and limited radiotherapy equipment, thus hindering
these early efforts. It was not until 1984 in Japan,2 that IORT
treatment techniques using megavoltage radiation produced
by a linear accelerator 共linac兲 became successful. Therefore,
modern IORT practice dates from the work of Abe et al.3 and
Abe and Takahashi4 in Japan published in the early 1970s
and 1980s. The practice of IORT was started in the United
States in the late 1970s by Goldson at Howard University,5
Gunderson et al. at Massachusetts General Hospital,6 and
Tepper and Sindelar7 and Fraas et al.8 at the National Cancer
Institute.
Initially, IORT flourished in both the academic and community hospital setting. In 1992, Coia and Hanks.9 reported
on a pattern-of-care study that indicated that of 1293 radiation oncology facilities in the United States, 108 reported
doing IORT, and 29 of those had two or more residents. With
approximately 90 residency training programs in existence at
that time, that means that roughly one third were performing
IORT. Fewer than 30 centers are now performing IORT. The
reasons for this decline in interest are twofold. First, establishing the usefulness of IORT as adjunct therapy has been
difficult. Single-institution experiences have suggested the
usefulness of IORT for primary T4 and recurrent rectal
retroperitoneal
sarcoma,14,15
pancreatic
cancer,10–13
16–18
and selected recurrent gynecologic19–21 and genicancer,
tourinary malignancies.22–25 Because of the difficulty in accruing large numbers of patients for these disease sites, it is
unlikely that phase III studies evaluating the utility of IORT
as a definitive therapeutic modality could be performed unless this were done on an international basis. The exception
could be in the area of breast cancer, where significant numbers of patients have already been treated in Europe. Second,
the majority of centers use their conventional linacs to perform IORT. In this case, the anesthetized patient must be
moved to a sanitized treatment room, accompanied by operating room 共OR兲 personnel. This is technically difficult and
relatively inefficient, with the linac often unavailable for
conventional treatment for a considerable time for room
preparation and waiting for the patient. The uphill battle
faced by proponents of IORT is the high cost of a dedicated
facility in the OR. A dedicated linac in an OR is no longer a
cost-effective option for any hospital when the costs of the
machine and radiation shielding are included.
The entry into the field of IORT of mobile linacs that can
be used in existing ORs with reduced shielding requirements
makes the cost and logistics of setting up an IORT program
much easier and therefore provides a stimulus to the field.
Two manufacturers of mobile linacs are Intraop Medical InMedical Physics, Vol. 33, No. 5, May 2006
1477
corporated of Santa Clara, California, which manufactures
the Mobetron, and Hitesys of Aprilia, Italy, which manufactures the Novac7. Currently, 26 mobile units are installed in
the United States and Europe.26 Thus, there has been a resurgence of interest in IORT in recent years.
By now, many of the new mobile units have been in operation for several years and we have gained important experience in mobile IORT technology. Although there are
many similarities between IORT treatments via stationary
units and mobile units, several important considerations are
unique to mobile units. This installed base of mobile linacs
and the degree of clinical activity that is currently being carried out motivates a review of all the physics procedures
associated with operating these units in a clinical setting.
The purpose of this Task Group 共TG-72兲 is to provide
sufficient information for a physicist to contribute to the
physical aspects of the planning process, such as room selection, estimation of required radiation shielding, and adequate
selection of treatment equipment for the prospective IORT
program, and to perform the required acceptance tests and
commissioning to bring one of these units into clinical operation. There are significant differences between the two
mobile systems in their mechanical design, acceleration
methodology, dosimetry, and docking. Both the Mobetron
and Novac7 are approved by the U.S. Food and Drug Administration 共FDA兲, although there are no Novac7 units currently operating in the United States. This report complements the work of previous Task Groups on IORT27 and
electron-beam dosimetry28,29 Due to space considerations,
we have abbreviated certain sections of the published version
of this report. The full unabridged version, with detailed illustrations, is available electronically.30
This Task Group has been careful to follow current
共AAPM兲 practice in the use of prescriptive injunctions such
as “must,” “shall,” and “should.” Imperatives such as “must”
or “shall” apply to matters of compliance with law or regulation. “Recommendations” are applied to procedures that
the Task Group deems important to follow, although a physicist may always choose alternatives after careful consideration. “Should” is used to identify suggested procedures to
address significant QA issues for which a variety of approaches are reasonable.
II. IORT USING MOBILE VERSUS STATIONARY
LINEAR ACCELERATORS
Stationary and mobile linacs for electron beam IORT have
many similarities. Both make use of shallow-penetrating radiation. Applicators are used to confine the beam to the volume of interest within the surgical area. Treatment is performed under sterile conditions with the patient anesthetized.
Radiation is delivered in a large single fraction. Multiple
fields may be used to treat different areas, treat larger fields,
or conform better to the target volume. Beam modifiers include bolus, placed at the end of the applicator or on the
patient surface, to increase surface dose 共with reduced beam
penetration兲, and absorbers such as lead, for shielding critical
1478
Beddar et al.: Task Group No. 72
structures or field matching.31–33 A typical IORT treatment
using a mobile unit has been described by Domanovic
et al.34 in detail in a case study in which IORT was used on
a patient with sigmoid carcinoma.
This report concerns differences in IORT with mobile
linacs. Some differences apply to any linac 共either mobile or
stationary兲 in a dedicated OR. Mobile units and dedicated
stationary units both permit treatment in a sterile OR. Special
treatment accessories are required for both units, including a
couch 共surgical bed兲 to facilitate patient setup. A primary
concern is radiation protection during treatment and daily
QA. Mobile IORT units are designed primarily for use in an
unshielded OR; therefore, exposure limits typically restrict
their use to the treatment of a small number of patients per
week plus the required daily QA and warmup. To prevent
excess exposure in adjacent rooms, especially on the floor
below, the maximum beam energy is limited to 10– 12 MeV,
limiting target coverage to a depth of a few centimeters. A
beam stopper is incorporated in some designs, which may
interfere with patient setup. In addition to an unshielded OR,
one must also plan for a facility for dosimetry and maintenance 共which can be the storage room兲 providing sufficient
structural shielding for commissioning, extended dosimetry
共e.g., annual calibrations or experiments兲, and maintenance
and adjustment contingencies. Some users have reduced this
need by performing preadjustment and commissioning at the
manufacturers’ facilities.
The application-specific design of mobile units can lead to
advantages over conventional units adapted to IORT. For example, electron beams could well have flatter beam profiles
than conventional linacs, and the range of motion of the
treatment head gives more flexibility in setting up the patient. On the other hand, limitations on these units are imposed by practical concerns of storage, transport, treatment
setup, and radiation protection.
Details that differ for mobile units in program implementation, including selection of the rooms required for the different procedures 共commissioning, treatment, and storage兲,
are dealt with in Sec. III. Radiation protection issues, arising
from the higher leakage and scatter in an unshielded OR, are
presented in Sec. IV. Differences in commissioning, including output calibration, are discussed in Sec. V.
III. IMPLEMENTATION OF AN IORT PROGRAM
WITHIN AN OPERATING ROOM ENVIRONMENT
A successful IORT program within an OR environment
requires careful planning, involving coordination of tasks
with timely and efficient communication among several departments. These departments generally include operative
services 共usually referred to as the OR兲, radiation oncology,
surgery, anesthesiology, and engineering. Depending on the
institution, the engineering support personnel may be part of
the radiation oncology department. The IORT team and the
role of each member of this team have been clearly defined
by Task Group 48 共Ref. 27兲 and therefore will not be dealt
with in this report. Other support personnel,27 such as houseMedical Physics, Vol. 33, No. 5, May 2006
1478
keeping, security staff, transport personnel, and elevator operators, will not be needed because the unit will be in the OR
where all IORT treatments will be delivered. Each department will have a significant role in the implementation of
such a multidisciplinary program. Consequently, a team approach should be embraced from the beginning.
Implementation of an IORT program using a mobile unit35
in the OR includes staff preparation, documentation of specialized procedures, and selection of the OR共s兲 and surgical
bed共s兲.
The following steps will facilitate smooth and efficient
implementation of a mobile IORT program:
共1兲 Interdepartmental meetings early in the planning phase,
involving all relevant departments.
共2兲 A site visit to an institution performing IORT using a
mobile system.
共3兲 A written proposal for program implementation, tailored
to the institution.
共4兲 Development of written procedures.
共5兲 Selection of the OR共s兲, storage room and dosimetry facility.
共6兲 Selection of the surgical bed共s兲.
共7兲 Education of staff involved in the IORT procedure and
OR staff peripheral to the program.
共8兲 Scheduled training in the OR.
共9兲 One or more “dry runs” before the first IORT procedure.
At the beginning of such a program, we believe it is important to have all members of the IORT team involved in all
of the initial procedures so they can go through the learning
process rapidly, implement the improved methods efficiently,
and reach optimum performance of IORT. The training of the
rest of the OR staff should follow once the initial IORT team
reaches an acceptable level of confidence. A complete discussion of these points is provided in the full electronic
report.30
IV. RADIATION PROTECTION
Mobile electron linacs are meant to be placed in existing
OR suites that have been constructed with no special shielding requirements. These systems are designed with the concept of being utilized to deliver radiation in nonshielded OR
rooms and are provided with a beam stopper.30 The beam
stopper for certain mobile IORT units is designed to track the
movement of the gantry in all directions so that it will always
intercept the primary beam, whereas other beam stoppers
must be manually positioned. Radiation leakage results
mostly from photon leakage, scatter, and x-ray contamination
from the electron beams. The electron scatter produced in the
OR has a limited range, and most conventional walls are
sufficient to stop the electron scatter produced in the OR.36
Therefore, radiation safety assessments for these mobile systems consist of performing radiation surveys around the ORs
that are intended to be used for IORT and limiting the number of IORT cases that can be performed in any given OR so
that the maximum exposure limits are not exceeded.
1479
Beddar et al.: Task Group No. 72
A. Regulatory considerations
Limits for radiation exposure of personnel are usually
regulated by national or state government agencies. In the
United States, the National Council on Radiation Protection
and Measurements.37 and the federal government promulgate
standards.38,39 In addition, standards may vary between countries or states and may change with time. This Task Group
共TG-72兲 believes the following to be absolute requirements:
共1兲 The most current exposure levels applicable to the geographic location 共country or state兲 of the mobile accelerator installation shall be adopted.
共2兲 The site plan must be approved by the appropriate regulatory agency before delivery of the unit takes place.
共3兲 A radiation survey must be performed for every OR
where the unit will be used and for any other room
where the unit could be used 共e.g., the dosimetry room兲.
共4兲 The survey must be performed for the highest electron
energy, the largest applicator, and for every anticipated
and possible clinical configuration of the unit.
共5兲 Electrical requirements should be evaluated for the ORs
selected for IORT, the storage area, and any other room
where the unit could be used.
共6兲 Floor load capacities should be evaluated for the rooms
selected for IORT, the storage area, any other room
where the unit could be used, and all possible transportation routes that could be used.
共7兲 Exposures accrued by personnel must be evaluated according to a radiation safety Quality Management
Program.
B. Radiation site plan
1. Treatment operating rooms
The manufacturer will ordinarily provide a threedimensional radiation leakage and scatter exposure profile
for the IORT unit. If the unit is capable of a range of motions, several profiles will be required to complete the site
plan properly. The anticipated workload of each mode and
energy will figure into the site plan. This workload, calculated for ORs, should include the MUs for machine warm-up
and daily QA but should not include the workload for commissioning and annual QA measurements 共see the following
section兲. Mills et al.40 calculated typical workload limits for
existing ORs using the Mobetron system and found that it is
possible to treat up to four patients per week in an existing,
unshielded OR. Therefore, it may be necessary to consider
more than one OR for IORT treatments if a higher patient
load is anticipated.
2. Commissioning and annual quality assurance
location
The shielding of a mobile accelerator is designed for infrequent use for IORT, not for continuous use in an unshielded room.40 Therefore, it is strongly recommended that
a dedicated vault or location for commissioning and annual
quality assurance activities be chosen. A separate site plan
Medical Physics, Vol. 33, No. 5, May 2006
1479
must be developed for the location chosen for commissioning and annual QA. Even an efficient commissioning will
require several hundred thousand MUs.40 An annual calibration will typically require less than 100 000 MUs. If occupied areas surround the intended location, the user needs to
identify the type of occupied areas, the occupancy factor, the
use factor, and the maximum exposure level allowed in each
of the areas by state regulations. If the vendor provides the
leakage data, the maximum workload during working hours
can be estimated accordingly. If the maximum workload
poses a problem in the acceptance testing and commissioning schedule, one solution is to conduct the procedures outside working hours and establish temporary controls on the
surrounding areas. The actual exposure should be measured
as soon as the mobile unit is able to generate a beam. The
measured exposure values should be used for final workload
limit calculations. The workload limit is determined by the
maximum allowable weekly or hourly exposure, whichever
is higher, in the adjoining area that receives the highest exposure. It is very important to get radiation safety personnel
involved in the process early. If the location chosen is not
sufficiently shielded and posted to be a controlled area, then
steps including temporary barriers and signs, are needed to
make it a controlled area during the time of these measurements.
C. Radiation survey
According to current regulatory limits in most states in
the United States, the allowable exposure level for uncontrolled areas is 1 mSv per year. This corresponds to a limit of
approximately 0.02 mSv per week. In addition, in a noncontrolled area, no more than 0.02 mSv is allowed during any
one hour. The regulatory limits allow controlled areas an
exposure of 50 mSv per year. This corresponds to a limit of
approximately 1 mSv per week. Controlled areas must be
labeled appropriately, and access by members of the public
must be restricted. The occupancy factor is 1 for controlled
areas in this environment. A radiation survey of the exposure
level at various locations outside the OR for the IORT unit
must be performed in every OR in which the unit will be
used. Regulatory agencies require these surveys for any external beam radiotherapy unit. The survey must be performed
for representative and anticipated worst-case situations of
possible clinical configurations of the unit. The measured
exposures are used to calculate the final operational limitations of the unit. A final operational plan must take into consideration the MUs generated during patient treatment,
warm-up, output, energy check, and adjustment contingencies. Considering an OR with no added shielding, it is common for only a very limited number of patients to be accommodated per week without exceeding regulatory limitations.
D. Exposure rate measurements
Daves and Mills36 performed a detailed analysis of the
shielding assessment on a Mobetron unit. Their method
should, in principle, be applicable to the Novac7. Their investigation provided a resource to assess shielding and pa-
1480
Beddar et al.: Task Group No. 72
tient load restrictions for any facility performing IORT with
units similar to the Mobetron. Their exposure rate measurements data indicated that the Mobetron may be operated in
an area with no shielding under a nominal patient load expectation. Assuming standard building materials, their results
demonstrated that a workload of three to four patients per
week in a given OR, including warmup, could be easily accommodated. Such workloads should be assessed for any
facility used and will be specific only to that facility. If mobile IORT units are to be used without workload limitations,
then they should only be used in shielded ORs.
V. ACCEPTANCE TESTING AND COMMISSIONING
This section provides guidance and practical recommendations on the acceptance testing and commissioning of mobile electron therapy units used for IORT. Published literature relevant to IORT with electron beams includes the Task
Group 2529 and Task Group 3941 reports on clinical electron
beam dosimetry, the TG-48 report27 on IORT using stationary linacs, Task Group 39 protocol41 and the Task Group 51
protocol28 for clinical reference dosimetry of high-energy
electron beams. However, several important considerations
in IORT accelerator acceptance testing and commissioning
procedures are unique to mobile accelerator units. For instance, the lengthy testing procedures that are normally carried out in the dedicated and shielded treatment room vaults
for stationary accelerators generally cannot be performed in
the heavily scheduled ORs designated for IORT. The radiation exposure rates from these procedures to areas adjacent
to the unshielded ORs would most likely exceed the acceptable exposure limits established for stationary accelerators. It
is best that these acceptance testing and commissioning procedures be carried out in an existing vault where available.
A. Acceptance testing measurements
A mobile IORT unit must pass acceptance testing according to the manufacturer’s specifications. The acceptance testing procedure for a mobile IORT unit includes the following:
共1兲
共2兲
共3兲
共4兲
共5兲
共6兲
Radiation survey.
Interlocks and safety features testing.
Mechanical testing.
Beam characteristics tuning.
Docking system test.
Options and accessories evaluation.
The radiation survey at the testing site is conducted as
soon as the accelerator is able to produce a stable beam and
after a preliminary output calibration. All surrounding areas,
including rooms one floor above and below, should be characterized in terms of occupancy factor and radiation control
classification 共controlled area or uncontrolled area兲 based on
the 10CFR20 report.38,39 The exposure rates in each of the
surrounding areas should be measured under the same irradiation conditions to be used for the acceptance testing procedures, especially with respect to the location of the accelerator in the room. The workload limit for the acceptance
and commissioning process can be calculated from the surMedical Physics, Vol. 33, No. 5, May 2006
1480
vey result and expressed in terms of MUs per hour. The
effect of the workload limit on the anticipated measurements
in the testing procedures should be analyzed ahead of time.
The total MUs needed for the testing procedures can be estimated based on the type of commissioning dosimetry data
to be taken and the measurement devices. For example, one
can make the following estimate of the total MUs needed
when a water scanner is used for beam profile and percentage
depth ionization measurements. Assuming the average scanning speed to be used is 5 mm/ sec and the average scan
length is 15 cm 共the maximum Mobetron applicator size is
10 cm兲, the beam-on time needed per scan tscan should be
less than 100 sec 共the actual time to scan 15 cm is 30 sec兲. If
one percentage depth ionization curve and one beam profile
will be measured per electron applicator and there are N
applicators, the total beam-on time for the ionization curve
and profile scanning is Tscan = 2N * tscan, which is
1600 sec–less than 30 min. If the accelerator has a nominal
MU rate of 1000 MU/ min, then 30 min of beam-on time
would require 30 000 MU per electron energy. The total
beam-on time required for the entire acceptance testing and
commissioning process can be estimated in units of Tscan.
The beam-on time for the above measurements is estimated
to be less than ten units of Tscan. If the workload limit significantly hinders the commissioning process with the use of
a water phantom, one can consider several options to shorten
the procedure. These options include: 共1兲 reducing the MU
usage when appropriate in the testing procedures by using a
low MU rate; 共2兲 replacing the water phantom scans with
film; and 共3兲 conducting measurements outside normal working hours.
All interlocks and safety features should be tested following the manufacturer’s acceptance testing procedures. One
should make sure that these interlocks and safety features,
including the emergency off switches, are operational during
the normal mode of operation of the unit 共e.g., the clinical
mode兲. The mechanical testing includes verifying the full
range of gantry motion, including rotational and translational
movements. The mechanical movements and controls of mobile IORT units differ significantly in design and function
from those of a conventional accelerator. The mechanical
movements of the gantry and treatment couch for a conventional accelerator are designed to rotate and translate with
respect to a fixed isocenter. In contrast, a mobile accelerator
will have no isocenter per se, and the geometric accuracy of
treatment delivery using a mobile unit will depend solely on
the accuracy of the docking. Once the electron applicator is
placed inside the patient and aligned to the intended treatment area, the operator should be able to control the gantry
movement in all directions available to achieve docking. The
proper operation of the beam stopper, if any, should also be
verified.
Beam tuning includes adjustments of the beam energy,
output rate, and flatness and symmetry of the reference applicator used for output calibration. The manufacturer’s installation engineer usually performs the task of beam tuning.
1481
Beddar et al.: Task Group No. 72
1481
FIG. 1. The soft-docking system used
by the Mobetron. 共a兲 The electron applicator, in contact with the tumor bed,
is rigidly clamped to the surgical bed
using a modified Bookwalter clamp.
共b兲 The gantry being moved for soft
docking to the applicator. 共c兲 The LED
display and electron applicator. The
green light in the center of the display
indicates that proper alignment has occurred and the gantry is properly
docked.
Note
the
air
gap
共4 cm± 1 mm兲 between the end of the
gantry and the top surface of the
applicator.
Relative output factors, flatness, and symmetry of all other
applicators should be measured afterward by clinical physicists.
Systems with soft docking, such as the Mobetron 共Fig. 1兲,
require acceptance testing of the docking system. The softdocking system, also referred to as air docking,27,42–45 is
more flexible than the hard-docking system of the Novac7
共Fig. 2兲, in which the coupling of the electron applicator to
the accelerator beam collimation system is direct and
rigid.46,47 For the Mobetron unit, the optical docking system
consists of a system of laser detecting devices mounted on
FIG. 2. The hard-docking system used by the Novac7. 共a兲 The accelerator
beam collimation system and electron applicator before docking. 共b兲 The
hard-docking mechanism. 共c兲 The docked unit, with the electron applicator
in contact with the tumor bed.
Medical Physics, Vol. 33, No. 5, May 2006
the accelerator beam collimation system to assist the operator in performing the soft docking of the gantry with the
electron applicator. The soft docking is achieved by adjusting
the gantry’s rotation angle, tilt angle, height, and two translational shifts 共longitudinal and lateral兲 of the gantry in the
horizontal plane. The status of each aspect of the alignment
is shown on a light-emitting diode 共LED兲 display on the
accelerator to guide the operator in the docking process.48
During irradiation, the docking is interlocked for both alignments of the treatment head with the applicator and for treatment distance. Optical coupling can be very sensitive to the
quality of the alignment, whereas the dosimetric quality of
the treatment is likely less sensitive. We recommend that the
clinical physicist evaluate the change in beam characteristics
at clinically realistic conditions when the soft docking is not
perfect in the commissioning process, when possible. Note
that FDA regulations might prevent the use of a mobile IORT
unit without the optical docking interlock. The TG-48
report27 included a suggestion to make allowances for misalignment in soft docking because precise alignment can be
time consuming and difficult to maintain in the presence of
applicator motion due to patient breathing. Hogstrom et al.49
recommended that the user perform measurements of beam
dosimetry sensitivity versus optical docking accuracy to determine the docking tolerance for clinical use.
All accessories supplied with the unit should be individually examined in the acceptance testing process prior to use.
The user should follow the manufacturer’s specifications and
tolerance in testing and examining the operation controls,
docking system, interlocks, accessories, and any optional devices.
Details of the mobile electron IORT unit acceptance tests
are specified in the acceptance test procedure document pro-
1482
Beddar et al.: Task Group No. 72
1482
TABLE I. Typical procedures required for acceptance testing of a mobile IORT unit.
Procedure
Radiation survey
Mechanical inspection
Radiation safety
Beam characteristics
Dosimetry system
Control console
Docking system
Options and accessories
Safety features
Comment
Ensure no individual is exposed to radiation levels in
violation of regulations, and verify the normal operation
of emergency off switches.
Verify the movement range, speed, control, and accuracy
of the gantry and beam stopper. Verify the physical sizes
of all applicators.
Verify dose attenuation through the beam stopper.
Verify beam energy, surface dose, dose rate, field
flatness, symmetry, and x-ray contamination according to
specifications. Verify beam energy constancy for all
gantry angles.
Verify the precision of the backup MU chamber, the
linearity and reproducibility of the MU chambers, and
the dosimetry interlocks.
Verify the normal function of each control on the control
console.
Verify the normal function of the optical docking system.
Verify normal function.
Examine all safety features 共emergency off, rad-on light,
and audible warning sounds兲.
vided by the manufacturer. Table I, which lists the items
included in the acceptance testing of Mobetron units, is
shown as an example.
B. Commissioning and dose measurements
The methodology and equipment that should be used in
the acceptance testing and commissioning of electron beams
for IORT units should follow the general recommendations
made in the TG-51 protocol for reference dosimetry on clinical electron beams.28 This Task Group 共TG-72兲 recommends
the use of a water phantom for the beam calibration as described by TG-51. The methods for obtaining relative dosimetry measurements are at the discretion of the responsible
clinical physicist, who must make the decision on the basis
of multiple considerations, including radiation safety, the
clinical accuracy needed for IORT treatment, commissioning
time frame, resources available, and the limitations and
availability of the measurement devices.
The beam characteristics commonly measured in the commissioning of a mobile IORT unit are listed in Table II.
This Task Group will not make any further recommendations as far as what type or model of ionization chamber or
detector should be used for clinical reference dosimetry, because this has been covered elsewhere27–29,41,50–52 However,
several unique aspects in the commissioning of a mobile
IORT unit deserve the user’s attention. Mobile IORT units
have dose rate outputs several times higher than conventional accelerators so that they can deliver large doses 共10 to
TABLE II. Typical measurements used in mobile IORT unit commissioning.
Measurements
Comment
Beam profiles 共depth dose
and cross plane profiles兲
Measurements are done for each applicator and beam
energy and should extend to regions outside the
treatment area.
Measurements are done for a limited sample of
applicators and beam energies 共including the highest
beam energy兲 and should be made lateral to the
applicator walls at various depths.
Applicator factors are relative to a 10-cm circular cone,
and the measurements are done at dmax for each
applicator and beam energy.
The air gap factor is the ratio of dose with an air gap to
the dose without one at dmax. Air gap factors are
measured at the appropriate depths of dmax for each
combination of applicator and beam energy.
Output calibration is done at the TG-51 reference depth
dref using the 10-cm circular applicator. From these
measurements the dose/MU at dmax is determined.
Leakage profiles
Applicator factors
Air gap factors
TG-51 output calibration
Medical Physics, Vol. 33, No. 5, May 2006
1483
Beddar et al.: Task Group No. 72
FIG. 3. The central axis percentage depth dose for a 10-cm circular applicator from a stationary linear accelerator 共Siemens ME, filled circles兲 and a
mobile linear accelerator 共Mobetron, open circles兲 for a 6-MeV electron
beam.
20 Gy兲 in a short time 共1 to 2 min兲. The ion recombination
correction factor Pion depends on the dose per pulse in accelerator beams and thus will change if either the pulse rate for
a fixed dose rate or the dose rate is changed.28,29,53 At the
high dose rates used by mobile IORT units, cylindrical chambers can have large values of Pion. For instance, the value of
Pion for a 共PTW兲 cylindrical chamber 共Model 30006, inner
radius 3.05 mm兲 exposed to a dose rate of 10 Gy/ min is
greater than 1.05. However, Pion did not exceed 1.03 for a
Markus PTW parallel plate chamber 共Model 23343, sensitive
volume 0.055 cm3兲. This Task Group recommends that
chambers with Pion values outside the acceptable range
specified by TG-51 should not be used for output calibration.
Furthermore, it is essential that the dose per pulse and
hence the dose rate be kept fairly stable during data collection, because Pion will no longer be constant and large fluctuations in the dose rate over time will therefore affect ionization measurements. For instance, when measuring
applicator output factors, it has been observed that, as the
dose rate changed from 10 to 15 Gy/ min over the course of
one hour, the ion recombination Pion also changed, and thus
the output factors appeared to be changing. However, in normal operation where the beam is not used continuously for
long time periods, the dose rate of a mobile linac is not
expected to vary significantly. For instance, Beddar54 examined the stability of a Mobetron linac over 20 quality assurance trials and found variation within ±2%. The author also
found that hours of inactivity, with the unit powered on 共in
standby mode兲 either throughout the day or overnight, led to
variations in output of about 1%.
Piermattei et al.55 found that, with high dose values of 30
to 60 mGy per pulse for the Novac7 共compared with 4 to
6 mGy per pulse for the Mobetron兲, the error in dose resulting from the use of a parallel plate chamber could be as high
as 20% due to overestimation of Pion. For different pulse
rates, they measured Pion from the ratio of the dose measured
by radiochromic film to that measured by the parallel plate
chamber uncorrected for ion recombination. Other users of
the Novac7,56 because of this ion recombination issue, have
Medical Physics, Vol. 33, No. 5, May 2006
1483
FIG. 4. The central axis percentage depth dose for a 10-cm circular applicator from a stationary linear accelerator 共Siemens ME, filled circles兲 and a
mobile linear accelerator 共Mobetron, open circles兲 for a 12-MeV electron
beam.
used chemical Fricke dosimeters, provided by the mailed dosimetry service at the Italian Primary Standard Dosimetry
Laboratory in Rome, and radiochromic films for dosimetry.
Di Martino et al.57 have determined the relationship between
Pion and the dose per pulse based on generalized Boag
theory. They found good agreement between percent depth
dose 共PDD兲 curves evaluated using Gafchromic films and
parallel-plate ionization chambers with values of Pion determined for doses of 30 to 130 mGy per pulse. This Task
Group recommends determining Pion using the standard twovoltage technique described in TG-51 for doses less than
10 mGy per pulse, and using an alternate method for higher
doses per pulse as suggested by the Novac7 users.55–57
Another aspect of commissioning a mobile IORT unit is
the lack of a gantry isocenter and a surgical bed with precise
movement control. Additional time is needed to set up a
water phantom. The beam stopper on a mobile IORT unit
may also prevent the use of the water phantom support sys-
FIG. 5. A beam profile at the depth of dmax for a 6-MeV electron beam from
a stationary linear accelerator 共Siemens ME, filled circles兲 compared with
beam profiles at the depth of dmax from a mobile linear accelerator 共Mobetron, open circles兲 for a 10-cm electron applicator.
1484
Beddar et al.: Task Group No. 72
1484
tissue close to the applicator. This was discussed in the
TG-48 report,27 which also included typical scans measured
lateral to the applicator walls.
VI. RECOMMENDED QUALITY ASSURANCE
Individual state regulations require certain QA practices
for medical linacs; these requirements differ from state to
state, and some may not be well suited to these specialpurpose devices. The physicist must ensure that the use of
mobile IORT equipment complies with any relevant regulations and/or apply for exemptions where justified.
FIG. 6. A beam profile at the depth of dmax for a 12-MeV electron beam
from a stationary linear accelerator 共Siemens ME, filled circles兲 compared
with beam profiles at the depth of dmax from a mobile linear accelerator
共Mobetron, open circles兲 for a 10-cm electron applicator.
tem 共e.g., table support兲 that normally comes with most commercial phantom scanners. It may be necessary to build a
special low table that straddles the beam stopper.
Figures 3 and 4 show the central axis depth dose curves
for 6- and 12-MeV electron beams, respectively, from a stationary linac 共Siemens兲 compared with those from a mobile
linac 共Mobetron兲 for a 10-cm electron applicator. All depth
dose curves were measured using the method described by
the TG-51 protocol28 The depth dose curves of the mobile
unit have a higher surface dose, which can be attributed to a
greater proportion of energy-degraded, scattered electrons in
the beam. Figures 5 and 6 show beam profiles at the depth
dmax for 6 and 12 MeV electron beams obtained from a conventional accelerator 共Siemens兲 and a mobile IORT unit
共Mobetron兲. The difference between the flatness and symmetry curves shown in Figs. 5 and 6 can be attributed to differences in the source-to-surface distance variation and the scattering foil design. The mobile units have smaller horns in
their beam profiles, a desirable feature for delivery of a uniform dose within an IORT field. Typical isodose distributions
for IORT mobile units are shown in Figs. 7 共Mobetron兲 and
8 共Novac7兲. Leakage beam profiles that extend beyond the
applicator walls are needed to estimate the dose to normal
A. Previous quality assurance recommendations for
medical linear accelerators
Any discussion of QA for mobile linacs used for IORT
must acknowledge the recommendations published in the
Task Group 40 report.58 regarding QA for medical linacs in
general. In addition, the TG-48 report27 discussed specific
QA issues for linacs used for IORT. Table III summarizes the
pertinent recommendations of these previous, complementary reports regarding dosimetric and mechanical QA.
B. Quality assurance for mobile electron accelerators
When adapting these recommendations to mobile accelerators, the clinical physicist needs to deal with some conflicting considerations. These units are partially disassembled
and transported each day of use. They forgo adjustable collimator jaws and eliminate bending magnets to reduce
weight and radiation leakage. These design elements simplify the system, but they make the electron beam energy
more dependent on variations in rf power generation and
coupling to the accelerator. Therefore, on one hand, there are
reasons to perform more frequent beam measurements than
with conventional installations. On the other hand, the equipment is used in ORs with little or no added shielding, so
radiation safety considerations argue for limiting the beam
time for QA as much as possible. These competing concerns
can be partially resolved by developing an efficient QA process, but they do present an ongoing challenge.
Output and energy can be checked efficiently with the use
of a dedicated solid phantom in which a dosimeter can be
FIG. 7. Typical isodose distributions
measured from the Mobetron for the
4- and 12-MeV beams using the largest applicator 共10-cm diameter兲, a
smaller applicator 共4-cm diameter兲,
and an applicator with a 30-deg bevel
共5-cm diameter兲.
Medical Physics, Vol. 33, No. 5, May 2006
1485
Beddar et al.: Task Group No. 72
1485
FIG. 8. Typical isodose distributions
from the Novac7 for 5- and 9-MeV
beams using an electron applicator
with a straight cone of 5 cm diameter
and for the 9-MeV beam using a 22.5deg beveled applicator with a 5-cm
diameter.
placed at two depths: near the depth of dose maximum and at
a point on the depth dose curve in the 50– 80% range. The
output constancy is taken from the measurement near dmax
and the energy constancy from the ratio of the two readings.
This Task Group recommends that for mobile accelerators,
the electron output constancy be checked each day of use.
The electron energy check should also be checked daily. If it
proves to be sufficiently consistent, then the physicist may
judge it reasonable to reduce the frequency to monthly after
properly documenting the energy consistency.
When judging how many MUs to apply to these measurements, the physicist needs to ensure that the beam runs long
enough to enable all interlocks. 共Some machines disable
some dosimetry interlocks during an initial period.兲
For a machine having four energies, a typical protocol is
to warm up the machine and dosimeter with about 400 MU
and then check the output and the electron energy for each
energy with single 200-MU readings. The total number of
MUs used for daily QA may exceed the number of MUs used
for treatment. Given that the machine is prepared for use
more often than it is actually used, more beam time 共and
ambient radiation兲 may be allocated to QA than to treatment.
Hence, there is good reason to carefully assess which readings and how many MUs per reading are necessary for QA.
Use of a dual channel dosimeter to simultaneously acquire
readings at two depths would be advantageous.
Both the accelerator characteristics and the docking
mechanism affect the flatness and symmetry of the treatment
fields. This is especially true for machines using soft-docking
mechanisms. This Task Group recommends that field flatness
should be checked monthly, in accordance with TG-40. The
docking apparatus should be checked for basic integrity each
day of use, in accordance with TG-48. This Task Group 共TG72兲 further recommends that the alignment of soft-docking
systems should be checked at least monthly. For systems that
use special attachments for routine QA, this Task Group recommends that, at least annually, the flatness and symmetry of
the beams should be checked in the soft-docked configuration used clinically.
For mobile systems, the practical question of when to set
up the machine and do the QA checks takes on added significance. As with any multidisciplinary, single-dose procedure, the tolerance for machine downtime is very low, but the
need to move and set up the machine adds complexity and
the possibility of malfunctions. Consequently, there can be
value to setting up and testing the basic operation of the
machine on the day before its intended use. Recommended
dosimetric QA can follow on the day of treatment, preferably
early enough to permit some troubleshooting if needed. This
is a labor-intensive process that can be simplified if experience with the machine demonstrates its reliability.
As for any radiation treatment equipment, annual QA
checks should repeat critical elements of the initial acceptance testing and commissioning. The task is likely to be
complicated by workload limitations, however, unless the
unit can be moved into a shielded environment. For example,
TABLE III. Summary of the quality assurance recommendations for electron accelerators made by previous task groups.
Parameter
Output constancy
Depth dose
Flatness and symmetry
Applicator output factors
Output versus gantry angle
Monitor chamber linearity
Docking mechanism
TG-40
3% tolerance for daily QA. 2% tolerance for monthly
and annual calibrations.
Range of energy ratios corresponding to 2-mm shift in
depth dose for monthly and annual calibrations.
3% tolerance for monthly checks. 2% tolerance for
annual calibrations.
2% tolerance, checks performed annually.
2% tolerance, checks performed annually.
1% tolerance, checks performed annually.
Not applicable.
TG-48
Follow TG-40.
Same as TG-40 for annual calibrations. Follow standard
departmental procedures for monthly calibrations.
Same as TG-40 for annual calibrations. Follow standard
departmental procedures for monthly calibrations.
Same as TG-40.a
None.
None.
To be checked each day of use.
TG-48 specifically recommended checking all applicators and energies with a tolerance of 2 – 3 % for a few years and then sampling 共Ref. 27兲 after that if
results warrant.
a
Medical Physics, Vol. 33, No. 5, May 2006
1486
Beddar et al.: Task Group No. 72
1486
TABLE IV. Summary of the quality assurance recommendations for mobile electron accelerators used for IORT.
Parameter
Day of use
Output constancy
Energy constancy
Door interlocks
Mechanical motions
Docking system
Monthly
Output constancy
Energy constancy
Flatness and symmetry constancy
Docking system
Emergency off
Annually
Output calibration for reference conditions
Percent depth dose for standard applicator
Percent depth dose for selected applicators
Flatness and symmetry for standard applicator
Flatness and symmetry for selected applicators
Applicator output factors
Monitor chamber linearity
Output, PDD, and profile constancy over
the range of machine orientations
Inspection of all devices normally kept sterile
it may be necessary to use film instead of a scanning water
phantom. If the initial commissioning and subsequent annual
QA tests are to be done in different environments with different dosimeters, then appropriate baseline measurements
should be done during the commissioning.
Table IV summarizes the QA recommendations for mobile electron accelerators used for IORT. The term “constancy” refers to agreement with original commissioning
data.
In addition to these elements of dosimetric and mechanical machine QA, there are aspects of procedural QA that
should be considered. In the OR environment, the attending
radiation oncologist will usually be scrubbed and may verbally indicate the key elements of the prescription 共applicator, energy, dose, etc.兲 to the person who will perform the
MU calculation and program the machine. There are two
likely sources of error in such a scenario. One is that the
treatment planner may misunderstand the physician’s verbal
instructions. Another is that the planner may make a mistake
in the calculation or in programming the treatment console.
The team tasked with clinically implementing IORT will
need to recognize this potential for error and design procedures accordingly. For example, the planner can use both
manual and computerized calculation methods, thus double
checking the mechanics of the calculation. In addition, the
calculation can be written out in such a way that the physiMedical Physics, Vol. 33, No. 5, May 2006
Tolerance
Action level
3%
Range of energy ratios
corresponding to 2-mm
shift in depth dose
Functional
Functional
Functional
Recommended
Recommended
2%
Range of energy ratios
corresponding to 2-mm
shift in depth dose
3%
Functional
Functional
Recommended
Recommended
2%
2 mm in depth over the
range of clinical interest
2 mm in depth over the
range of clinical interest
2%
3%
2–3 %
1%
As above
Required
Required
Functional
Recommended
Recommended
Recommended
Recommended
Recommended
Recommended
Recommended
Required
Recommended
Recommended
Recommended
Recommended
Recommended
cian can check that the prescription has been properly understood. Finally, a second person, such as the physician or
another physicist, can check that the energy and MUs have
been properly programmed. Having more than one person
check the critical elements in a single-shot procedure is crucial.
The Radiation Therapy Oncology Group continues to
sponsor the Radiological Physics Center 共RPC兲 QA program
for interinstitutional clinical trials. TG-48 recommended in
its report27 that the RPC TLD service be used as part of an
outside, independent check on an institution’s dosimetry.
This Task Group 共TG-72兲 reemphasizes that recommendation and strongly recommends institutions using mobile accelerators to use the services of RPC, before the initiation of
treatments if possible.
As part of a comprehensive QA program, the annual review should include an assessment of clinical procedures and
radiation safety procedures, maintenance history, and spare
parts inventory.
VII. CLINICAL ASPECTS OF IORT TREATMENT
DELIVERY: DOSE SPECIFICATION
Traditionally, IORT procedures performed under the Radiation Therapy Oncology Group protocol have specified
that the 90% isodose line covers the target volume, whereas
1487
Beddar et al.: Task Group No. 72
the International Commission on Radiation Units 共ICRU兲
and Measurements Report 35 共Ref. 59兲 recommends that the
dose be prescribed at dmax. Therefore, TG-48 recommended
that both the 90% dose and the maximum dose should be
reported. Since the publication of the TG-48 report, neither
the ICRU nor any other institution has achieved a formal
agreement on dose specification for IORT. However most
IORT groups follow the convention of prescribing to the
90% isodose level to ensure coverage of the target by the
90% isodose line. This Task Group recommends that the
dose be prescribed at the 90% isodose level and then the
dose be reported at both the 90% level and dmax.
VIII. RECOMMENDATIONS FOR FUTURE
CONSIDERATIONS
Many aspects of IORT are still in an investigative and less
standardized state than external beam radiation therapy.
Therefore, in existing IORT programs, several centers have
developed specialized applicators,4,8,42,45,47,60,61 alignment
aids,62 and other technical equipment to adapt to institutional
methods or requirements, such as patient case selection and
surgical techniques. For instance, the treatment of extended
tumor sites 共e.g., sarcomas located on extremities兲 may require the development of applicators and techniques for field
abutment.8 Other design features of mobile IORT machines
may limit the development of some specialized equipment.
Adaptations of site-developed equipment, and possibly advice by the manufacturer, may be necessary to allow for the
use of the soft-docking aids provided with the linacs.
The management of cancer using IORT is limited to the
delivery of one single dose during surgery, which is an occasional modality that can hardly be postponed or repeated.
Therefore, machine interlocks, which exclude patient treatment, should be restricted to those that are necessary to warrant patient safety and to avoid machine damage. Interlocks
of lower priority 共e.g., those that are triggered by slight applicator misalignments or machine instability兲 should be well
documented and their effect on the dose distribution well
quantified so that, if necessary, an override can be considered
at the time of treatment. Apart from few early phantom measurements on beam inclination and gaps,33,42,49 the effects of
beam misalignment, gaps, bolus, changes of penumbra, and
tissue inhomogeneities in realistic patient geometries are not
well investigated. Further research is needed in these areas,
and further development is necessary in the treatment planning of IORT for realistic patient geometries.
ACKNOWLEDGMENTS
The members of TG-72 wish to thank the following
physicists for their contributions concerning the Novac7: Giampiero Tosi and Mario Ciocca, Istituto Europeo di Oncologia, Milano, Italy, Assunta Petrucci, Azienda Complesso San
Filippo Neri, Rome, Italy, and Axel Schmachtenberg, Department of Radiation Oncology, University Clinics, Aachen,
Germany. We thank M. Saiful Huq of the University of PittsMedical Physics, Vol. 33, No. 5, May 2006
1487
burgh Cancer Institute, James M. Balter of the University of
Michigan, and Rasika Rajapakshe of the British Columbia
Cancer Agency for their detailed reviews of this report. We
also acknowledge M. Saiful Huq for helpful teleconference
discussions and suggestions with the Task Group. Finally, we
thank the members of the Radiation Therapy Committee of
the AAPM chaired by Michael G. Herman.
a兲
Electronic address: abeddar@mdanderson.org
C. Beck, “On external Roentgen treatment of internal structures 共eventration treatment兲,” N. Y. Med. Journal 89, 621–622 共1909兲.
2
M. Abe, “Intraoperative radiotherapy – past, present and future,” Int. J.
Radiat. Oncol., Biol., Phys. 10, 1987–1990 共1984兲.
3
M. Abe, M. Fukuda, K. Yamano, S. Matsuda, and H. Handa, “Intraoperative irradiation in abdominal and cerebral tumours,” Acta Radiol.
10, 408–416 共1971兲.
4
M. Abe and M. Takahashi, “Intraoperative radiotherapy, The Japanese
experience,” Int. J. Radiat. Oncol., Biol., Phys. 7, 863–868 共1981兲.
5
A. Goldson, “Preliminary clinical experience with intraoperative radiotherapy 共IORT兲,” Semin. Oncol. 8, 59–65 共1978兲.
6
L. L. Gunderson, W. U. Shipley, and H. D. Suit, “Intraoperative irradiation a pilot study external beam photons with ‘boost’ dose intraoperative
electrons,” Cancer 49, 2259–2266 共1982兲.
7
J. Tepper and W. F. Sindelar, “Summary of the workshop on intraoperative radiation therapy,” Cancer Treat. Rep. 65, 911–918 共1981兲.
8
B. A. Fraass, R. W. Miller, T. J. Kinsella, W. F. Sindelar, F. S. Harrington,
K. Yeakel, J. Van de Geijn, and E. Glatstein, “Intraoperative radiation
therapy at the National Cancer Institute, technical innovation and dosimetry,” Int. J. Radiat. Oncol., Biol., Phys. 11, 1299–1311 共1985兲.
9
L. R. Coia and G. E. Hanks, “The need for subspecialization intraoperative radiation therapy,” Int. J. Radiat. Oncol., Biol., Phys. 24, 891–893
共1992兲.
10
L. L. Gunderson, D. M. Nagorney, D. C. McIlrath, J. M. Fieck, H. S.
Wieand, A. Martinez, D. J. Pritchard, F. Sim, J. A. Martenson, J. H.
Edmonson, and J. H. Donohue, “External beam and intraoperative electron irradiation for locally advanced soft tissue sarcomas,” Int. J. Radiat.
Oncol., Biol., Phys. 25, 647–656 共1993兲.
11
S. Nag, J. Mills, E. Martin, C. Bauer, and J. Grecula, “IORT using highdose-rate brachytherapy or electron beam for colorectal carcinoma,”
Front. Radiat. Ther. Oncol. 31, 238–242 共1997兲.
12
Y. Hashiguchi, T. Sekine, H. Sakamoto, Y. Tanaka, T. Kazumoto, S. Kato,
M. Sakura, Y. Fuse, and Y. Suda, “Intraoperative irradiation after surgery
for locally recurrent rectal cancer,” Dis. Colon Rectum 42, 886–893;
discussion 893–895 共1999兲.
13
N. J. Sanfilippo, C. H. Crane, J. Skibber, B. Feig, J. L. Abbruzzese, S.
Curley, J. N. Vauthey, L. M. Ellis, P. Hoff, R. A. Wolff, T. D. Brown, K.
Cleary, A. Wong, T. Phan, and N. A. Janjan, “T4 rectal cancer treated
with preoperative chemoradiation to the posterior pelvis followed by multivisceral resection: patterns of failure and limitations of treatment,” Int. J.
Radiat. Oncol., Biol., Phys. 51, 176–183 共2001兲.
14
C. G. Willett, H. D. Suit, J. E. Tepper, H. J. Mankin, K. Convery, A. L.
Rosenberg, and W. C. Wood, “Intraoperative electron beam radiation
therapy for retroperitoneal soft tissue sarcoma,” Cancer 68, 278–283
共1991兲.
15
P. W. Pisters, M. T. Ballo, M. J. Fenstermacher, B. W. Feig, K. K. Hunt,
K. A. Raymond, M. A. Burgess, G. K. Zagars, R. E. Pollock, R. S.
Benjamin, and S. R. Patel, “Phase I trial of preoperative concurrent doxorubicin and radiation therapy, surgical resection, and intraoperative
electron-beam radiation therapy for patients with localized retroperitoneal
sarcoma,” J. Clin. Oncol. 21, 3092–3097 共2003兲.
16
T. J. Kinsella and W. F. Sindelar, “Intraoperative radiotherapy for pancreatic carcinoma. Experimental and clinical studies,” Cancer 78, 598–604
共1996兲.
17
W. F. Sindelar and T. J. Kinsella, “Studies of intraoperative radiotherapy
in carcinoma of the pancreas,” Ann. Oncol. 10 Suppl 4, 226–230 共1999兲.
18
C. H. Crane, A. S. Beddar, and D. B. Evans, “The role of intraoperative
radiotherapy in pancreatic cancer,” Surg. Oncol. Clin. N. Am. 12, 965–
977 共2003兲.
19
M. A. Mahe, J. P. Gerard, J. B. Dubois, A. Roussel, E. Bussieres, M.
Delannes, F. Guillemin, T. Schmitt, D. Dargent, Y. Guillard, P. Martel, P.
Richaud, J. C. Cuilliere, J. De Ranieri, and L. Malissard, “Intraoperative
1
1488
Beddar et al.: Task Group No. 72
radiation therapy in recurrent carcinoma of the uterine cervix: report of
the French intraoperative group on 70 patients,” Int. J. Radiat. Oncol.,
Biol., Phys. 34, 21–26 共1996兲.
20
J. P. Gerard, G. Collin, L. Ayzac, D. Dargent, D. Raudrant, F. N. Gilly, P.
Romestaing, I. Sentenac, and R. Coquard, “The role of IORT as salvage
therapy for recurrent cervical and endometrial carcinoma,” Front. Radiat.
Ther. Oncol. 31, 260–262 共1997兲.
21
R. Martinez-Monge, M. Jurado, J. J. Aristu, M. Moreno, M. Cambeiro, A.
Perez-Ochoa, G. Lopez-Garcia, and J. L. Alcazar, “Intraoperative electron
beam radiotherapy during radical surgery for locally advanced and recurrent cervical cancer,” Gynecol. Oncol. 82, 538–543 共2001兲.
22
E. G. Shaw, L. L. Gunderson, J. K. Martin, R. W. Beart, D. M. Nagorney,
and K. C. Podratz, “Peripheral nerve and ureteral tolerance to intraoperative radiation therapy: clinical and dose-response analysis,” Radiother.
Oncol. 18, 247–255 共1990兲.
23
F. A. Calvo, J. J. Aristu, O. Abuchaibe, J. Rebollo, O. Fernandez Hidalgo,
J. Zudaire, J. M. Berian, and I. Azinovic, “Intraoperative and external
preoperative radiotherapy in invasive bladder cancer: effect of neoadjuvant chemotherapy in tumor downstaging,” Am. J. Clin. Oncol. 16,
61–66 共1993兲.
24
F. A. Calvo, J. Aristu, I. Azinovic, R. Martinez, M. Santos, D. Ortiz de
Urbina, and J. M. Berian, “关Intraoperative radiotherapy with accelerated
electrons for urinary bladder carcinoma: principles and results兴,” Arch.
Esp. Urol., 52, 649–654 共1999兲.
25
M. G. del Carmen, B. Eisner, C. G. Willet, and A. F. Fuller, “Intraoperative radiation therapy in the management of gynecologic and genitourinary malignancies,” Surg. Oncol. Clin. N. Am. 12, 1031–1042 共2003兲.
26
A. S. Beddar and S. Krishnan, “Intraoperative radiotherapy using a mobile linear electron accelerator: A retroperitoneal sarcoma case,” J. Appl.
Clin. Med. Phys. 6, 95–107 共2005兲.
27
J. R. Palta, P. J. Biggs, D. J. Hazle, M. S. Huq, R. A. Dahl, T. G. Ochran,
J. Soen, R. R. Dobelbower, and E. C. McCullough, “Intraoperative electron beam radiation therapy, technique, dosimetry, and dose specification,
report of Task Group 48 of the radiation therapy committee, American
Association of Physicists in Medicine,” Int. J. Radiat. Oncol., Biol., Phys.
33, 725–746 共1995兲.
28
P. R. Almond, P. J. Biggs, B. M. Coursey, W. F. Hanson, M. S. Huq, R.
Nath, and D. W. O. Rogers, “AAPM’s TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams,” Med. Phys.
26, 1847–1870 共1999兲.
29
F. M. Khan, K. P. Doppke, K. R. Hogstrom, G. J. Kutcher, R. Nath, S. C.
Prasad, J. A. Purdy, M. Rozenfeld, and B. L. Werner, “Clinical electron
beam dosimetry, Report of AAPM radiation therapy committee Task
Group 25,” Med. Phys. 18, 73–109 共1991兲.
30
A. S. Beddar, P. J. Biggs, S. Chang, G. A. Ezzell, B. A. Faddegon, F. W.
Hensley, and M. D. Mills, “Intraoperative radiation therapy using mobile
electron linear accelerators: Report of AAPM Radiation Therapy Committee Task Group No. 72 共unabridged electronic version兲,” 共AAPM,
2006兲.
31
E. C. McCullough, “Intraoperative Electron Beam Radiation Therapy
共IORT兲,” in Radiation Oncology Physics—1990. American Association of
Physicists in Medicine, Medical Physics Monograph No. 19, edited by J.
A. Purdy 共American Institute of Physics, New York, 1992兲, pp. 480–490.
32
E. C. McCullough and P. J. Biggs, “Physical Aspects of Intra-Operative
Electron Beam Irradiation, in Intraoperative Radiation, Techniques and
Results, edited by L. L. Gunderson, C. G. Willett, L. B. Harrison, and F.
A. Calvo 共Humana Press, New Jersey, 1999兲.
33
P. J. Biggs, E. R. Epp, C. C. Ling, D. H. Novack, and H. B. Michaels,
“Dosimetry field shaping and other considerations for intra-operative
electron therapy,” Int. J. Radiat. Oncol., Biol., Phys. 7, 875–884 共1981兲.
34
M. A. Domanovic, M. Ouzidane, R. J. Ellis, T. J. Kinsella, and A. S.
Beddar, “Using intraoperative radiation therapy—A case study,” AORN
J. 77, 412–417 共2003兲.
35
A. S. Beddar, M. L. Kubo, M. A. Domanovic, R. J. Ellis, T. J. Kinsella,
and C. H. Sibata, “A new approach to intraoperative radiation therapy,”
AORN J. 74, 500–505 共2001兲.
36
J. L. Daves and M. D. Mills, “Shielding assessment of a mobile electron
accelerator for intraoperative radiotherapy,” J. Appl. Clin. Med. Phys. 2,
165–173 共2001兲.
37
“Limitation to Exposure from Ionizing Radiation, NCRP Report 116”
共National Council on Radiation Protection and Measurements, Bethesda,
MD, 1993兲.
38
U.S. Nuclear Regulatory Commission, “Title 10 Code of Federal ReguMedical Physics, Vol. 33, No. 5, May 2006
1488
lations 20.1201” 共U.S. Government Printing Office, Washington, D.C.,
1998兲.
39
U.S. Nuclear Regulatory Commission, “Title 10 Code of Federal Regulations 20.1301共a兲” 共U.S. Government Printing Office, Washington, D.C.,
1998兲.
40
M. D. Mills, L. C. Fajardo, D. L. Wilson, J. L. Daves, and W. J. Spanos,
“Commissioning of a mobile electron accelerator for intraoperative radiotherapy,” J. Appl. Clin. Med. Phys. 2, 121–130 共2001兲.
41
P. R. Almond, F. H. Attix, L. J. Humphries, H. Kubo, R. Nath, S. Goetsch,
and D. W. O. Rogers, “The calibration and use of plane-parallel ionization
chambers for dosimetry of electron beams: An extension of the 1983
AAPM protocol report of the AAPM Radiation Therapy Committee Task
Group No. 39,” Med. Phys. 21, 1251–1260 共1994兲.
42
J. R. Palta and N. Suntharalingam, “A nondocking intraoperative electron
beam applicator system,” Int. J. Radiat. Oncol., Biol., Phys. 17, 411–417
共1989兲.
43
H. Kharrati, P. Aletti, and F. Guillemin, “Design of a non-docking intraoperative electron beam applicator system,” Radiother. Oncol. 33, 80–83
共1994兲.
44
D. Jones, E. Taylor, J. Travaglini, and S. Vermeulen, “A non-contacting
intraoperative electron cone apparatus,” Int. J. Radiat. Oncol., Biol., Phys.
16, 1643–1647 共1989兲.
45
P. Björk, T. Knöös, P. Nilsson, and K. Larsson, “Design and dosimetry
characteristics of a soft-docking system for intraoperative radiation
therapy,” Int. J. Radiat. Oncol., Biol., Phys. 47, 527–533 共2000兲.
46
N. Papanikolaou and B. Paliwal, “The study of the effect of cone shielding on intraoperative radiotherapy,” Med. Phys. 22, 571–575 共1995兲.
47
R. A. Price and K. M. Ayyangar, “IORT apparatus design improvement
through the evaluation of electron spectral distributions using Monte
Carlo methods,” Med. Phys. 27, 215–220 共1999兲.
48
A. S. Beddar, M. A. Domanovic, M. L. Kubo, R. J. Ellis, C. H. Sibata,
and T. J. Kinsella, “Mobile linear accelerators for intraoperative radiation
therapy,” AORN J. 74, 700–705 共2001兲.
49
K. R. Hogstrom, A. L. Boyer, A. S. Shiu, T. G. Ochran, S. M. Kirsner, F.
Krispel, and T. A. Rich, “Design of metallic electron beam cones for an
intraoperative therapy linear accelerator,” Int. J. Radiat. Oncol., Biol.,
Phys. 18, 1223–1232 共1990兲.
50
P. Björk, T. Knöös, and P. Nilsson, “Measurements of output factors with
different detector types and Monte Carlo calculations of stopping-power
ratios for degraded electron beams,” Phys. Med. Biol. 49, 4493–4506
共2004兲.
51
P. Björk, P. Nilsson, and T. Knöös, “Dosimetry characteristics of degraded
electron beams investigated by Monte Carlo calculations in a setup for
intraoperative radiation therapy,” Phys. Med. Biol. 47, 239–256 共2002兲.
52
A. S. Beddar and R. C. Tailor, “Calibration of low-energy electron beams
from a mobile linear accelerator with plane-parallel chambers using both
TG-51 and TG-21 protocols,” Phys. Med. Biol. 49, N105–N110 共2004兲.
53
J. W. Boag and J. Currant, “Current Collection and Ionic Recombination
in Small Cylindrical Ionization Chambers Exposed to Pulsed Radiation,”
Br. J. Radiol. 53, 471–478 共1980兲.
54
A. S. Beddar, “Stability of a mobile electron linear accelerator system for
intraoperative radiation therapy,” Med. Phys. 32, 3346–3349 共2005兲.
55
A. Piermattei, S. delle Canne, L. Azario, A. Russo, A. Fidanzio, R.
Miceli, A. Soriani, A. Orvieto, and M. Fantini, “The saturation loss for
plane parallel ionization chambers at high dose per pulse values,” Phys.
Med. Biol. 45, 1869–1883 共2000兲.
56
M. Ciocca, R. Orecchia, C. Garibaldi, E. Rondi, A. Luini, G. Gatti, M.
Intra, P. Veronesi, R. Lazzari, G. Tosi, and U. Veronesi, “In vivo dosimetry using radiochromic films during intraoperative electron beam radiation therapy in early-stage breast cancer,” Radiother. Oncol. 69, 285–289
共2003兲.
57
F. Di Martino, M. Giannelli, A. C. Traino, and M. Lazzeri, “Ion recombination correction for very high dose-per-pulse high-energy electron
beams,” Med. Phys. 32, 2204–2210 共2005兲.
58
G. J. Kutcher, L. Coia, M. Gillin, W. F. Hanson, S. Leibel, R. J. Morton,
J. R. Palta, J. A. Purdy, L. E. Reinstein, G. K. Svensson, M. Weller, and
L. Wingfield, “Comprehensive QA for radiation oncology, Report of
AAPM Radiation Therapy Committee Task Group 40,” Med. Phys. 21,
581–618 共1994兲.
59
“ICRU Report 35. Radiation Dosimetry: Electron beams with energies
between 1 and 50 MeV” 共International Commission on Radiation Units
and Measurements, Bethesda, MD, 1984兲.
60
I. Sentenac, J. P. Gerard, N. Salerno, G. De Laroche, and X. Montbarbon,
1489
Beddar et al.: Task Group No. 72
“Intraoperative Radiation Therapy,” in Radioterapia e Trattamenti Integrati 共Casa Editrice Ambrosiana, Milano, 1988兲, pp. 49–55.
61
C. E. Nyerick, T. G. Ochran, A. L. Boyer, and K. Hogstrom, “Dosimetry
characteristics of metallic cones for intraoperative radiotherapy,” Int. J.
Medical Physics, Vol. 33, No. 5, May 2006
1489
Radiat. Oncol., Biol., Phys. 21, 501–510 共1991兲.
F. J. Prott, N. Willich, S. Palkovic, C. Horch, and H. Wassmann, “A new
method for treatment planning and quality control in IORT of brain tumors,” Front. Radiat. Ther. Oncol. 31, 97–101 共1997兲.
62